sm3.go

package sm3

import (
	"encoding/binary"
	"hash"
)

// digest represents the partial evaluation of a checksum.
type digest struct {
	h   [8]uint32
	x   [chunk]byte
	nx  int
	len uint64
}

func (d *digest) Write(p []byte) (int, error) {
	nn := len(p)
	d.len += uint64(nn)
	if d.nx > 0 {
		n := copy(d.x[d.nx:], p)
		d.nx += n
		if d.nx == chunk {
			block(d, d.x[:])
			d.nx = 0
		}
		p = p[n:]
	}
	if len(p) >= chunk {
		n := len(p) &^ (chunk - 1)
		block(d, p[:n])
		p = p[n:]
	}
	if len(p) > 0 {
		d.nx = copy(d.x[:], p)
	}

	return nn, nil
}

// Sum appends the current hash to b and returns the resulting slice.
// It does not change the underlying hash state.
func (d *digest) Sum(b []byte) []byte {
	// Make a copy of d so that caller can keep writing and summing.
	d0 := *d
	hash := d0.checkSum()

	return append(b, hash[:]...)
}

// Reset resets the Hash to its initial state.
func (d *digest) Reset() {
	d.h[0] = iv0
	d.h[1] = iv1
	d.h[2] = iv2
	d.h[3] = iv3
	d.h[4] = iv4
	d.h[5] = iv5
	d.h[6] = iv6
	d.h[7] = iv7

	d.nx = 0
	d.len = 0
}

// Size returns the number of bytes Sum will return.
func (d *digest) Size() int {
	return Size
}

// BlockSize returns the hash's underlying block size.
// The Write method must be able to accept any amount
// of data, but it may operate more efficiently if all writes
// are a multiple of the block size.
func (d *digest) BlockSize() int {
	return BlockSize
}

func (d *digest) checkSum() [Size]byte {
	len := d.len
	// Padding. Add a 1 bit and 0 bits until 56 bytes mod 64.
	var padding [64]byte
	padding[0] = 0x80
	if len%64 < 56 {
		d.Write(padding[0 : 56-len%64])
	} else {
		d.Write(padding[0 : 64+56-len%64])
	}

	// Length in bits.
	len <<= 3
	binary.BigEndian.PutUint64(padding[:], len)
	d.Write(padding[0:8])

	if d.nx != 0 {
		panic("d.nx != 0")
	}

	var digest [Size]byte

	binary.BigEndian.PutUint32(digest[0:], d.h[0])
	binary.BigEndian.PutUint32(digest[4:], d.h[1])
	binary.BigEndian.PutUint32(digest[8:], d.h[2])
	binary.BigEndian.PutUint32(digest[12:], d.h[3])
	binary.BigEndian.PutUint32(digest[16:], d.h[4])
	binary.BigEndian.PutUint32(digest[20:], d.h[5])
	binary.BigEndian.PutUint32(digest[24:], d.h[6])
	binary.BigEndian.PutUint32(digest[28:], d.h[7])

	return digest
}

// New returns a new hash.Hash computing the SHA256 checksum.
func New() hash.Hash {
	d := new(digest)
	d.Reset()
	return d
}

func Sum(data []byte) [Size]byte {
	var d digest
	d.Reset()
	d.Write(data)
	return d.checkSum()
}